Processing steps used in the semiconductor industry include depositing and etching films on a substrate. Dielectric films are deposited into complex topologies during some processing steps often to provide physical and electrical separation between conductive or semiconductive regions.
Many techniques have been developed to deposit dielectrics into narrow gaps including chemical vapor deposition techniques which sometimes employ plasma excitation. High-density plasma (HDP)-CVD has been used to fill many geometries due to the perpendicular impingement trajectories of the incoming reactants and the simultaneous sputtering activity. Some very narrow gaps have continued to develop voids due, in part, to the lack of mobility following initial impact. Reflowing the material after deposition can fill the void but, if the dielectric has a high reflow temperature (like SiO2), the reflow process may also consume a non-negligible portion of a wafer's thermal budget.
By way of its high surface mobility, flowable materials such as spin-on glass (SOG) have been useful in filling some of the gaps which were incompletely filled by HDP-CVD. SOG is applied as a liquid and cured after application to remove solvents, thereby converting material to a solid glass film. The gap-filling (gapfill) and planarization capabilities are enhanced for SOG when the viscosity is low. Unfortunately, low viscosity materials may shrink significantly during cure. Significant film shrinkage results in high film stress and delamination issues, especially for thick films.
Separating the delivery paths of two components can produce a flowable film during deposition on a substrate surface. FIG. 1 shows a schematic of a substrate processing system with a substrate 115 supported on a pedestal 110 affixed to a pedestal shaft 105. The substrate processing system has separated precursor delivery channels 125 and 135. An organosilane precursor may be delivered through one channel and an oxidizing precursor may be delivered through the other. The oxidizing precursor may be excited by a remote plasma 145 unit. The mixing region 120 of the two components occurs closer to the substrate 115 than alternative processes utilizing a more common delivery path. Since the films are grown rather than poured onto the surface, the organic components needed to decrease viscosity are allowed to evaporate during the process which reduces the shrinkage affiliated with a cure step. Growing films this way limits the time available for adsorbed species to remain mobile, a constraint which may result in deposition of nonuniform films. A baffle 140 or a showerhead (not pictured) may be used to more evenly distribute the precursors in the reaction region.
Gapfill capabilities and deposition uniformity benefit from high surface mobility which may be enabled by plasma excited oxygen radicals introduced from remote plasma unit 145. Precautions may be necessary to ensure that production of plasma excited oxidizer is sufficient and predictable.